The last week has been a notable one for our understanding of animal life, thanks to two very different research papers appearing within a couple of days of each other.

One continued a tradition of surprises from the octopus – and generated headlines around the world. Scientists Eric Edsinger and Gül Dölen gave octopuses the “party drug” MDMA, or ecstasy, and found that on the drug they were more inclined to approach other octopuses, and also interacted less cautiously, initiating more body contact.

The ecstasy experiment was small – using just four animals – and what resulted might have several different explanations. (The octopuses were always given their drugs after being tested without drugs in the same setting, and whenever experiences are ordered in time in this way, this can have its own effects. Some confusion resulting from the drug is possible, too, if the human case is any guide.) But it does seem that the octopuses, despite their vastly different brains, behaved in ways with surprising analogies to humans – especially in their willingness to initiate physical closeness, and general playfulness.

With the aid of genetic analysis, revealing a gene that probably affects these behaviours both in us and octopuses via the brain chemical serotonin, Edsinger and Dölen suggest that this research indicates that some mechanisms controlling social behaviour are very old in evolutionary terms – we last shared a common ancestor with octopuses well over 500m years ago. Whether those conclusions can be drawn about social life is unclear at this stage. This might be a situation where some ancient biological machinery can have a variety of roles in different organisms, sometimes helping to control social life, and sometimes doing other things, but perhaps often involving some form of exploration, evaluation and attraction.

This research adds to our own slowly evolving sense of what kinds of experience might be possible within animals far removed from us. Invertebrate animals had long been almost ignored when thinking about sentience and animal experience. But this is changing. Robert Elwood’s recent work has revealed good evidence that crustaceans such as crabs and shrimp can feel something like pain, and a study by Jean Alupay and others showed that octopuses tend and protect injuries on their arms. None of this work is decisive, but it all contributes to a picture in which a wide range of animals experience events as welcome or unwelcome. The ecstasy study complements this by exploring an elusive side of octopus behaviour – the side populated by inclinations, moods, and emotions. This is another hint that it will, in time, be possible to know what it’s like to be an animal very distant from ourselves.

The second paper that appeared last week came out of a rather different style of research. Ilya Bobrovskiy, a student at the Australian National University, abseiled down a cliff in a remote part of Russia and chopped out hunks of stone that contained the remains of a famously enigmatic organism, Dickinsonia. As Bobrovskiy suspected, the rocks contained not just ordinary fossils, but naturally mummified remains of its tissue.

Dickinsonia is one of the “Ediacaran” fossils, from more than 550m years ago, traces of a menagerie of beings that might in many cases be animals, but look as much like seaweeds, bathmats, flowers and lilypads (though they could not really have been plants). Dickinsonia was especially controversial, and has been interpreted in a range of different ways. But in those Russian rocks, Bobrovskiy and his colleagues found remains of cholesterol, an animal product used to build animal cell membranes.

Dickinsonia, however bathmat-like it may be, now takes a definite place among the animals, living at an overture stage in animal evolution, before a flurry of more familiar forms appeared in the Cambrian explosion. Dickinsonia is unlikely to be an ancestor of ours, or of octopuses, but it perhaps lived not long after the time of that last ancestor that octopuses shared with humans.

Of the animals found on Earth today, one that had already been picked out as a possible relative is Trichoplax, a tiny, flat, filmy, creature that is unusual among animals for having no nervous system at all. Despite this, it can creep along surfaces and feed, and its genome shows it has many of the components that are brought together to form nervous systems in animals like us. (The role of serotonin, if any, does not yet seem to be known.)

Animals are built from a unified, ancient kit of tools and materials, though from these resources, as Darwin said, endless and vastly different forms – octopus, Dickinsonia, human – have evolved.

• Peter Godfrey-Smith is professor of history and philosophy of science at the University of Sydney, and is the author of Other Minds: The Octopus and the Evolution of Intelligent Life